1. Field of the Invention
The present invention relates to an optical element incorporated in an optical device used in combination with a semiconductor laser, for example, and to an optical isolator using the optical element.
2. Related Art
An optical isolator produced using an optical element where a Faraday rotator and polarization glasses produced by orientationally dispersing with metal anisotropically-shaped particles in a glass substrate are bonded together is used for example in a semiconductor laser module as an optical device. (See “Applied Optoelectronics Handbook”, PP. 77-78 edited by editorial committee for Applied Optoelectronics Handbook, Shokodo).
An optical isolator is typically required to have isolation characteristic (extinction ratio) of 25 dB or higher.
Therefore, a polarization glass used for this purpose is also required to have isolation characteristic of 25 dB or higher. As anisotropically-shaped particles (typically silver or copper particles) are arranged in the vicinity of a surface of the glass substrate in this polarization glass, backscattering of incident light (i.e. a phenomenon that reflection light returns to the direction of incident light) occurs depending on used particles.
If the thickness of a layer oriented with anisotropically-shaped particles is simply reduced, a problem is caused, i.e., isolation characteristic of the polarization glass is lowered to less than 25 dB. If particles are oriented intensively in a thin layer (less than 10 μm) in order to increase the isolation, backscattering is increased.
Therefore, when such a polarization glass is bonded to a Faraday rotator, light scattering occurs on a surface of the Faraday rotator and in the layer of the polarization glass where anisotropic particles are orientationally dispersed, so that isolation characteristic is affected and deteriorated.